1. Field of the Invention
The present invention relates to an image region designation device and method which designates a necessary region in a radiological image and a radiological image processing device and method which performs a gradation process for a radiological image.
2. Description of the Related Art
A radiological image used in an image diagnosis is acquired by an imaging process of a computed radiography (CR) system or an imaging process using a radiation detector (FPD). The dynamic range of the acquired radiological image is very wide. When the entire dynamic range of the radiological image with a wide dynamic range is converted into an image, the contrast of the image is reduced and is not suitable for diagnosis. Therefore, image processing, such as a gradation process or a frequency enhancement process, is performed in order to adjust the dynamic range of the radiological image such that the concentration and contrast of the image to be displayed are appropriate. As a gradation processing method, for example, a method has been proposed which calculates a histogram of the pixel values of a radiological image, switches an algorithm or parameters on the basis of supplementary information, such as a captured part of the radiological image, an imaging direction, and the age of a subject, creates a portion (main histogram) corresponding to a main region of the histogram, and allocates a gradation curve such that the concentration range of the main histogram falls in the dynamic range of a display device. In addition, a method has been proposed which sets a region of interest (ROI) in a featured region of a radiological image, switches an algorithm or parameters on the basis of supplementary information of the radiological image, and allocates a gradation curve such that a reference value (for example, a maximum value or a median value) of the pixel value in the ROI is a predetermined concentration (for example, JP1994-61325B (JP-H06-61325B)).
However, in the above-mentioned method, since the supplementary information, such as the captured part of the radiological image, the imaging direction, and the age of the subject, is required, it is necessary to input the supplementary information of the radiological image to an image processing device which performs image processing whenever a radiological image is captured. Here, the operator who performs an imaging operation selects an imaging menu in the image processing device and inputs the supplementary information. For example, in general, about 100 to 300 imaging menus are used and the number of imaging menus varies depending on facilities. Therefore, the operation of selecting a desired imaging menu is very complicated depending on the operator who performs an imaging operation, which is likely to cause an input error. In addition, it is necessary to set optimal image processing parameters in each imaging menu in order to perform optimal image processing and an adjustment operation for setting the parameters is also very complicated. Furthermore, a radiology information system (hereinafter, referred to as a RIS) is introduced to allocate an imaging menu to imaging order information. In this case, it is not necessary to perform an imaging menu input operation. However, in the case of facilities without a RIS, the operator needs to perform the imaging menu input operation whenever an imaging operation is performed.
A large hospital has a full-time operator who is in charge of image processing. Therefore, when the quality of a radiological image is not satisfied, it is easy to correct the radiological image. However, it is difficult for a small hospital to employ the full-time operator who is in charge of image processing and it is very difficult to correct the radiological image such that the same quality as that obtained by the full-time operator who is in charge of image processing is obtained. Therefore, it is preferable to provide an image processing device which can automatically convert an image so as to be suitable for diagnosis, regardless of a subject or imaging conditions (for example, a tube voltage, a dose, and positioning).
JP4844560B, JP2004-364336A, and JP1996-331385A (JP-H08-331385A) disclose a method which extracts a region of interest from a radiological image and converts the gradation of the radiological image such that the concentration of the extracted region is a desired value. The method disclosed in JP4844560B extracts the bone part or the soft part included in a radiological image as the region of interest, weights the extracted region of interest to generate a weighted image, multiplies the radiological image by the weighted image to create a weighted histogram, evaluates the weighted histogram using a predetermined evaluation function, calculates a shift value of the histogram at which the evaluation value is the maximum, and determines image processing conditions in which a predetermined processing result is obtained at a pixel value of the radiological image corresponding to the maximum value of the evaluation function where the shift value is obtained, particularly, image processing conditions in which the pixel value corresponding to the shift value is a desired concentration value. The method disclosed in JP4844560B extracts the region of interest from the image, without using the supplementary information of the image and determines the image processing conditions for each image on the basis of the extracted region. Therefore, it is possible to obtain a radiological image subjected to the gradation process, without inputting an imaging menu.